The present invention relates to transmissions for use in vehicles, such as work vehicles, having an HST (hydrostatic transmission).
Shortening the longitudinal length of the vehicle is demanded commonly of various work vehicles in order to diminish the turning radius, improve the ease of driving and achieve cost reductions. The same demand is made on vehicles wherein the power of an engine or like drive source is transmitted to the drive axle via an HST, especially on work vehicles which are equipped with a work device externally of the vehicle body.
However, the conventional vehicles having the HST still remain to be improved in fully meeting this demand. The problems encountered with conventional work vehicles having the HST will be described with reference to a mower tractor of the front mount type.
With reference to FIG. 12 showing the conventional work vehicle, power transmission between an HST 100 and an engine 101 arranged from the front rearward longitudinally of the body of the vehicle is effected through a pump shaft 100a projecting rearward from the HST 100 and an engine drive shaft 101a projecting forward from the engine 101 and connected to the shaft 100a by a shaft.
Since the engine 101 is installed on the vehicle body with rubber vibration isolators interposed therebetween, a vibration difference occurs between the engine 101 and the HST 100. Accordingly, to interconnect the two components by a shaft with the vibration difference absorbed, the engine drive shaft 101a is connected to the pump shaft 100a by universal joints 102. With the conventional construction, therefore, the engine 101 needs to be disposed toward the rear so as to obtain a distance L between the rear end face of the HST 100 and the front end face of the engine 101 for arranging the two universal joints in series, consequently increasing the overall length of the vehicle.
Although it is possible to install the engine above the HST to shorten the overall vehicle length, this entails the need to upwardly shift the position of the driver""s seat and other members which are located above the engine, leading to impaired stability of the vehicle during driving owing to the rise of the center of gravity of the vehicle.
Especially with the work vehicle equipped with a work device 106 externally thereof among other vehicles, it is further desired that a transmission shaft 104 connecting a PTO (power take-off) shaft 103 to the input shaft 106a of the work device 106 be disposed horizontally to the great possible extent to prevent the joints of the transmission shaft 104 from giving off noise and assure the joints of improved durability.
To meet such a demand, for example JP-U No. 56555/1993 and JP-A No. 204135/1990 disclose an arrangement wherein the PTO shaft 103 is positioned below a front axle 105 and caused to project from the front end face of the front axle case (as indicated at X in FIG. 12) with use of power transmission means such as pulleys for use in work vehicles. The arrangement disclosed in these publications needs to lengthen the transmission shaft 104 (as indicated at Y in FIG. 12) if it is attempted to position the transmission shaft 104 closer to a horizontal while causing the PTO shaft 103, as positioned approximately at the same level as the engine output shaft 101a, to project from the front end of the front axle case, consequently increasing the overall vehicle length. Alternatively, the transmission shaft needs to be inclined (as indicated at Z in FIG. 12) if an attempt is made to shorten the overall vehicle length while causing the PTO shaft 103 to project from the front end of the front axle case at substantially the same level as the engine output shaft 101a, consequently impairing the durability of the transmission shaft. The arrangement disclosed is provided in view of these problems.
With the conventional construction described, a differential gear unit is provided between the engine output shaft 101a (or HST output shaft) and the PTO shaft, so that the power transmission between the two shafts must be so constructed as to clear the differential gear unit. This results in the drawback of making the power transmission complex to thereby increase the vehicle cost and impair the maintenance work efficiency.
An object of the present invention is to provide a transmission mechanism of simple construction for use in a work vehicle having an HST, the transmission mechanism serving to shorten the overall length of the vehicle while preventing the rise of the center of gravity of the vehicle.
Another object of the invention is to provide a transmission mechanism of simple construction for use in a work vehicle having an HST and equipped with a work device which is disposed externally of the vehicle body, the transmission mechanism serving to shorten the overall length of the vehicle while permitting a transmission shaft interconnecting a PTO shaft for driving the work device and an input shaft of the work device to be positioned close to a horizontal to the greatest possible extent.
The above objects can be fulfilled by a transmission mechanism for a vehicle having a power transmission path for transmitting power from a drive source installed in a vehicle body through an HST disposed away from the drive source toward a first direction longitudinally of the vehicle body at least to a differential gear unit for driving axles toward the first direction, the transmission mechanism being characterized in that:
a transmission is provided between the HST and the differential unit, the transmission having a casing, an input shaft connected to a drive shaft of the drive source by a shaft, and a first output shaft coupled to the differential gear unit, the input shaft extending from the casing toward a second direction opposite to the first direction,
the HST comprising a hydraulic pump having a pump shaft extending into the transmission casing, and a hydraulic motor cooperative with the hydraulic pump and having a motor shaft extending into the transmission casing,
the transmission comprising as housed in the casing a mechanical cooperating mechanism coupling the input shaft to the pump shaft and coupling the motor shaft to the output shaft to provide the power transmission path.
The foregoing objects can be fulfilled also by a transmission mechanism for a work vehicle including a vehicle body having one side toward a first direction along the length thereof and the other side toward a second direction opposite to the first direction, the work vehicle comprising a differential gear unit for driving axles positioned toward the first direction, an HST and a drive source which are arranged in the vehicle body from the first direction side toward the second direction, the work vehicle being equipped with a work device positioned toward the first direction externally thereof, the transmission mechanism having a travel power transmission path for transmitting power from the drive source to the differential gear unit through the HST, and a PTO power transmission path for dividedly transmitting power from the travel power transmission path to a PTO shaft for driving the work device, the transmission mechanism being characterized in that;
a transmission is provided between the differential gear unit and the HST, the transmission comprising a casing, an input shaft for receiving the power from the drive source, and a first output shaft coupled to the differential gear unit, the casing having a main portion facing the differential gear unit and an extension extending from the main portion toward one side of the vehicle body widthwise thereof, the PTO shaft projecting from the transmission extension toward the first direction and positioned outwardly of the differential gear unit toward one side of the vehicle widthwise thereof, the transmission casing having housed therein a travel cooperating mechanism and a PTO cooperating mechanism providing the travel power transmission path and the PTO power transmission path respectively.